Heavy tracked vehicles and skid steer vehicles benefit from numerous advantages coming from the use of bands when traction is needed, when compared to the sole use of wheels. One of the most important advantages is the provision of a better traction on all types of soil: rocky, uneven, muddy or covered with snow, etc. When traction is ensured via the use of a band, a sprocket usually transmits mechanical power from the engine to the traction band, which in turns transmits this power to the ground to provide movement to the vehicle. Therefore, the traction band's efficiency greatly relies on the interaction between the sprocket and the band, and more particularly, on the meshing of the drive lugs with the sprocket.
For metallic tracks, this interaction is extremely solid since the sprocket engages in the band according to the chain drive principle. The meshing efficiency of the sprocket with metallic bands benefits from the high strength and rigidity of steel. However, metallic tracks have drawbacks (high overhaul costs, damages to the ground, weight, noise, etc.) which led to the development of the reinforced elastomeric traction band technology.
By minimizing these drawbacks, the use of elastomeric materials for traction bands generated other problems which particularly concern the meshing of the sprocket and the traction band. These problems include teeth skipping, detracking and they are, among other reasons, attributable to the high elasticity of elastomeric materials.
In order to diminish the occurrences of these problems, it is possible to rigidify the elastomeric material by thickening the drive lugs. However, this solution is limited by the increased interference occurrences when a thickened drive lug meshes with its corresponding sprocket cavity. When the meshing occurs, it must be understood that the traction lug of the band must necessarily have a shape which allows the transit of the lug from a linear motion to a circular motion, in order to obtain a maximal traction. In fact, the ideal meshing process would be obtained if there were no friction nor interference.
Similar principles were applied for the development of the elastomeric traction band designed for defense or skid steer vehicles. It has been found that a similar traction lug profile seems to offer a worthwhile solution to such vehicles, since in usual driving conditions (constant speed on a flat ground), the induced tension in the traction band allows the preservation of a firm contact between the traction lugs and the sprocket.
However, these ideal conditions are rarely encountered by such vehicles equipped with elastomeric traction bands, especially since they are often subject to frequent and brutal accelerations and decelerations, and because they very often ride on inclined and irregular terrains. Thus, those extreme operating conditions, generating large tangential forces transmitted to the traction lugs by the sprocket, sometimes cause the deformation (crushing or stretching) of the traction lugs meshed in the sprocket, therefore changing the actual distance between consecutives lugs (pitch variation). The bench test measurements and the numerical simulations we have done show that the pitch variations can go up to ¼ inch for a lug pitch of 3 to 5 inches. These pitch variations induce important interferences and friction forces between the lug-sprocket assembly which, when combined to a tension decrease in the traction band, are sufficient to generate radial forces which can initiate de-tracking occurrences and teeth skipping. In these conditions and for those instances, it is not possible to solve this problem by modifying the lug profile or thickening the traction lugs.
It was suggested in the prior art to use exterior lug profiles on elastomeric traction bands not perpendicularly oriented with respect to the longitudinal axis of the traction band. For instance, see U.S. Pat. No. 6,068,354 (Akiyama et al.) and U.S. Pat. No. 5,984,438 (Tsunoda et al.). However, no prior art uses or even suggests the utilization of traction band with traction lugs configured in a chevron pattern or otherwise not parallel to the longitudinal axis of the traction band.